EyeTrackShop tested ads with different placement surrounded by identical content on a desktop, an iPhone, and an iPad, and it found that users with iPhones (and, by extension, other smartphones) were the least likely to see ads on Facebook, with only a 3 percent to 13 percent chance of being seen if they were located “below the fold.”

Ads on the desktop are located in fixed positions, according to EyeTrackShop, giving them more of a chance to be seen. In fact, the company found that desktop ads were the second destination respondents turned their eyes to, adding that their performance has improved since the introduction of timeline.

Mobile ads, in contrast, were seen by fewer people, with less time spent on them and significantly lower recall.

The iPad, however, presented an exception to the rule, as its larger display area actually resulted in better performance than Web ads. EyeTrackShop found that iPad ads were seen by 18 percent more people, who spent 29 percent longer viewing them, and were recalled at a similar level to Web ads.